1. Field of the Invention
This invention relates to an adsorbent mainly comprising a mixture of a carbonized material and a soil either as it is or in a shaped or granulated form and to a method of removing various contaminants occurring in water and air using the adsorbent.
2. Prior Art
Solid adsorbents such as activated charcoal have been widely used so far for the removal of toxic substances and trace contaminants occurring in water and air. However, such adsorbents each have a very strong selectivity with respect to substances adsorbable thereon. Therefore, it is very difficult to efficiently remove all contaminants from actual water or air which usually occurs as a complex pollution system in which a number of substances much differing in chemical characteristics coexist. In the case of activated charcoal, for instance, which is used most generally, the adsorbency for alkaline substances, such as ammonia and amines, and for colored substances, such as dye particles, is very weak and, in many instances, the contaminant concentration in water or air after passage through an activated charcoal-containing filtration layer differs little from the concentration before entering said filtration layer. In the activated charcoal method, when the contaminant and turbidity component fraction in water or air to be treated changes in composition, as substances having a higher affinity for activated charcoal than the substances adsorbed earlier on the surface of activated charcoal enter the layer, the phenomenon of replacement of the already adsorbed substances by the late comer contaminants takes place on the activated charcoal surface with ease. Thus, the new comer contaminants cause abrupt release, from the activated charcoal surface and from the system, of large amounts of contaminants already adsorbed and accumulated on the activated charcoal surface. Transitory but abrupt contaminant release due to such phenomenon causes very high concentration contamination as compared with the concentrations in water or air to be treated. Such high concentration recontamination is encountered frequently in actual adsorption plants using activated charcoal and offers a serious problem.
Furthermore, the mechanisms of trapping target components on known solid adsorbents such as activated charcoal always consist in adsorption of substances on the adsorbent surface and adsorption of substances on the adsorbent micropore inside surface. Therefore, once those surfaces have been covered with contaminants and coexisting substances, the adsorbing power rapidly decreases or is lost. While the time until such decrease in adsorbing power takes place depends on the characteristics and concentrations of target substances, said time is generally very short with samples from actual working sites, namely as short as 1/3 to 1/5 of the nominal value given by manufacturers. This is due to the above-mentioned simultaneous adsorption of coexisting substances. Upon such saturation of an adsorbent in respect to adsorption, it becomes necessary to immediately replace it with a fresh adsorbent. However, since the adsorbents in practical use are usually very expensive and the replacing work is laborious, such adsorbents are generally used continuously even after saturation in respect to adsorption without exchange until the lapse of a period indicated by manufacturers. However, the value indicated by manufacturers is based on the value measured in laboratories using specific substances possibly occurring in water or air to be treated without taking into consideration the possible effects of coexisting substances. As a result, the life of an adsorbent in the treatment of a complex system in an actual plant is much lower than the value given by the relevant manufacture.
As mentioned above, the solid adsorbents currently in use, such as activated charcoal, are quite powerless in many instances in adsorptively purifying actual foul water or contaminated air in which substances differing in chemical characteristics such as polarity coexist. In many cases, activated charcoal adsorbent layers become concentration layers. Such situation shows that frequent adsorbent exchange is inevitable in the conventional methods. In view of the above, development of a more effective adsorbent capable of trapping a broad range of substance groups with large adsorption or trapping capacity as well as marked prolongation of the adsorbent life in practical use or development of an adsorbent capable of self-regenerating or self-restoring the adsorption capacity thereof is waited for.